The present invention relates to a method for forming contacts, and particularly, relates to a method for forming memory contacts on a semiconductor device.
Most integrated circuits are manufactured by repeating several semiconductor processes, e.g. photolithographing, etching, depositing and doping, and are accomplished with many layers. To transmit signals among those layers, contacts and conductive lines are indispensable to modern semiconductor processes, especially for manufacturing memory chips. The contacts in a memory at least include bit-line contacts and gate contacts, and their manufacturing quality has great effect upon functions of the memory.
FIGS. 1xcx9c4 show the steps for forming contacts on a semiconductor device in the prior art. The contacts are positioned on a substrate 102 which has a bit-line contact area 100 and a gate contact area 200. FIG. 1A shows the bit-line contact area 100 which includes a first polysilicon layer 104, a conductive layer 106, a first dielectric layer 108, a side wall 110, a second dielectric layer 112, a third dielectric layer 114, a fourth dielectric layer 116 and a second polysilicon layer 118. FIG. 1B shows the gate contact area 200 which includes a third polysilicon layer 204, the conductive layer 106, a fifth dielectric layer 208, the fourth dielectric layer 116 and the second polysilicon layer 118.
Referring to FIG. 1A and FIG. 1B, the method of the prior art coats a photoresist 120 on the bit-line contact area 100 as well as the gate contact area 200, and then etches the two areas. Hence, a bit-line contact is formed on the bit-line contact area 100 as FIG. 2A shows; however, a gate contact is not formed yet insofar as FIG. 2B shows. The method of the prior art needs further steps of coating another photoresist 210 on the gate contact area 200, as FIG. 3A shows, and then etching the fifth dielectric layer 208 to form the gate contact as FIG. 3B shows.
This kind of semiconductor process causes the aspect ratio too small to facilitate photoresist removal.
The present invention provides a method for forming contacts on a semiconductor device, especially for forming memory contacts. The contacts mentioned herein are positioned on a substrate having a bit-line contact area and a gate contact area.
The method of the present invention includes the steps of forming an opening on the gate contact area, depositing a dielectric layer on the bit-line contact area and the opening, coating a photoresist to define a bit-line contact opening on the bit-line contact area and a gate contact opening on the gate contact area, etching the dielectric layer while using the photoresist as a mask to form the bit-line contact opening and the gate contact opening, removing the photoresist, and forming a conductive layer on the bit-line contact opening and the gate contact opening.